The invention relates to a system for transferring a load from ship-based production and storage units to dynamically positioned tankers, comprising a loading hose which, during a loading operation, extends between an end of the ship-based unit and a bow manifold on the tanker, and which is stored on the ship-based unit when not in use.
In connection with offshore loading of oil from so-called FSO and FPSO vessels, i.e. vessels for floating storage of oil (FSO=Floating Storage and Offloading) and for floating production and storage of oil (FPSO=Floating Production, Storage and Offloading), it is advantageous, especially in exposed ocean areas, to use DP-based buoy loading tankers (DP=dynamic positioning) in order to maintain a high continuity/loading regularity also in periods of bad weather.
FIG. 1 of the drawings schematically shows how ship and equipment typically is arranged to carry out such operations. The figure shows a ship-based storage and/or production unit 1 (i.e. an FSO or FPSO vessel) which is anchored by means of a turret anchoring 2, for example a so-called STP buoy, and a DP buoy loading tanker 3, wherein a loading hose 4 for the transfer of oil extends between the rearward end 5 of the unit 1 and a bow manifold 6 and an associated mooring arrangement on the tanker 3. The prevailing weather direction is designated xe2x80x9cWxe2x80x9d in the Figure.
The loading hose 4 typically is stored on a large hose reel 7 on the FSO/FPSO vessel 1 when the buoy loading tanker is not moored to the vessel.
The distance L1 between the tanker 3 and the vessel 1 typically is about 80 m. The distance between the vessels to some extent is delimited by the length of the hose 4. This is, inter alia, due to the fact that a long hose will require a larger hose reel 7, and also a stronger winch equipment on board the buoy loading tankers. When the tanker 3 is loading, the loading hose 4 hangs like a catenary between the vessel 1 and the manifold 6 on the tanker.
It is to be remarked that the DP-operated tanker 3 very often is connected to the FSO/FPSO vessel 1 lying in front by means of a mooring hawser 8, as shown in FIG. 1. The mooring hawser is stored on a hawser winch 9 on the vessel 1. The function of the mooring hawser is to prevent the hose 4 from being overloaded in cases wherein the distance between the vessels unintentionally becomes too large.
Traditionally, the mooring hawser 8 normally is placed in the region around the centre or fore-and-aft axis of the FSO/FPSO vessel, as illustrated in FIG. 1.
Experience shows that such DP loading is a very efficient loading method under marginal weather conditions. For example, a DP tanker will be able to carry out loading operations in waves having a significant wave height of Hs=5.5-6 m, as compared to a corresponding wave limitation of Hs=3.5-4 m for ships without DP.
However, it has occurred several times that DP ships move ahead in an uncontrolled manner. This type of occurrence, which is considered to be very critical since a contact or collision then might occur between the two vessels, is referred to in the field as xe2x80x9cposition drop outxe2x80x9d. Therefore, there is a need for a system which reduces the risk of possible damage effects in case of an occurring xe2x80x9cposition drop outxe2x80x9d.
Thus, it is an object of the invention to provide a load transferring system which reduces to a substantial degree the risk of contact/collision between the moored vessels during a loading operation, and which also gives the possibility of reducing the damage extent if a contact/collision nevertheless should occur.
A further object of the invention is to provide such a system which involves a simplification of the equipment forming part of the load transferring arrangement.
For achievement of the above-mentioned objects there is provided a system of the introductorily stated type which, according to the invention, is characterised in that the ship-based unit at said end is provided with two manifold and connecting means located at either side of the fore-and-aft axis of the unit, and that the ends of the loading hose are arranged for connection to a respective one of the connecting means, so that the hose, in connected condition, can hang like a catenary between the connecting means transversely to the ship-based unit, and an optional end of the hose can be released from the connecting means in question, to be connected to the bow manifold on the relevant tanker.